Size-selective polymer system

ABSTRACT

A size-selective hemocompatible porous polymeric adsorbent system is provided, the polymer system comprises at least one polymer with a plurality of pores, and the polymer has at least one transport pore with a diameter from about 250 Angstroms to about 2000 Angstroms, and the polymer has a transport pore volume greater than about 1.8% to about 78% of a capacity pore of volume of the polymer.

RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.11/601,931 filed on Nov. 20, 2006 now U.S. Pat. No. 7,875,182 entitled“Size Selective Hemoperfusion Polymeric Adsorbents”.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to size selective polymer system and inparticular, polymer systems having a plurality of pores with transportpores and a negative ionic charge on its surface.

The size-selective porous polymeric adsorbents of this invention arebiocompatible and hemocompatible and are designed to function in directcontact with body fluids. These adsorbents are useful in conjunctionwith hemodialysis for extracting and controlling the blood level ofβ₂-microglobulin without significantly perturbing the levels of albumin,immunoglobulins, leukocytes, erythrocytes, and platelets. Thesepolymeric adsorbents are also very effective in extracting cytokinesassociated with the systemic inflammatory response syndrome (SIRS), fromthe blood and/or physiologic fluid, in patients with sepsis, burns,trauma, influenza, etc. while keeping the physiologically requiredcomponents of blood at clinically acceptable levels.

2. Description of Related Art

Techniques of extracorporeal blood purification are important in manymedical treatments including hemodialysis, hemofiltration,hemoperfusion, plasma perfusion and combinations of these methods.Hemodialysis and hemofiltration involve passing whole blood throughhollow fibers to remove excess water and compounds of small molecularsize but are unable to remove protein toxins such asbeta-2-microglobulin (B2M) and the cytokines. Hemoperfusion is passingwhole blood over an adsorbent to remove contaminants from the blood.Plasma perfusion is passing blood plasma through an adsorbent. Inhemoperfusion, the treated whole blood returns to the patient's bloodcirculation system.

In addition to the common requirements such as hemocompatibility andsterility for medical devices, an ideal adsorbent for hemoperfusion andplasma perfusion should have an adsorption capacity and selectivityadequate for adsorbing toxins to the exclusion of useful components inorder to be beneficial to the patient.

Conventional adsorbing materials include activated carbon, silicates,diatomite and synthetic porous resins. Activated carbon has beenreported in extracorporeal adsorption for treating schizophrenia(Kinney, U.S. Pat. No. 4,300,551; 1981). Various synthetic polymericadsorbents have been disclosed for removing toxic shock syndrometoxin-1, bradykinin and endotoxin from blood (Hirai, et al. U.S. Pat.No. 6,315,907; 2001; U.S. Pat. No. 6,387,362; 2002, and U.S. Pat. No.6,132,610; 2000), and for removing poisons and/or drugs from the bloodof animals (Kunin, et al., U.S. Pat. No. 3,794,584; 1974). Adsorption bythe above adsorbents is generally rather nonselective and, therefore, islimited to short term treatments.

Most commercial porous resins are synthesized either by macroreticularsynthesis (Meitzner, et al., U.S. Pat. No. 4,224,415; 1980), such asAmberlite XAD-4® and Amberlite XAD-16® by Rohm and Haas Company or byhypercrosslinking synthesis [Davankov, et al. J. Polymer Science,Symposium No. 47, 95-101 (1974)], used to make the Hpersol-Macronet®resins by Purolite Corp. Many conventional polymeric adsorbents have alarge pore surface and adsorption capacity but a lack of selectivity dueto the broad distribution of pore sizes. Others are produced to adsorbsmall organic molecules or are not hemocompatible and therefore are notsuitable for selective adsorption of midsize proteins directly from bodyfluids.

In order to enhance the hemocompatibility, many techniques involvecoating the hydrophobic adsorbent with hydrophilic materials such aspolyacrylamide and poly(hydroxyethylmethacrylate) (Clark, U.S. Pat. No.4,048,064; 1977; Nakashima, et al., U.S. Pat. No. 4,171,283; 1979). Acopolymer coating of 2-hydroxyethyl methacrylate with diethylaminoethylmethacrylate is reported by Watanabe, et al. (U.S. Pat. No. 5,051,185;1991). Davankov, et al. (U.S. Pat. No. 6,114,466; 2000) disclosed amethod of grafting to the external surface of porous polymeric beadshydrophilic monomers including 2-hydroxyethyl methacrylate,N-vinylpyrrolidinone, N-vinylcaprolactam and acrylamide. Recently,Albright (U.S. Pat. No. 6,884,829 B2; 2005) disclosed the use of surfaceactive dispersants [including polyvinyl alcohol, poly(dimethylaminoethylmethacrylate), poly(vinylpyrrolidinone), and hydroxethylcellulose]during macroreticular synthesis to yield a hemocompatible surface onporous beads in a one step synthesis.

The internal pore structure (distribution of pore diameters, porevolume, and pore surface) of the adsorbent is very important toadsorption selectivity. A cartridge containing a packed bed of adsorbentwith effective pore diameters ranging from 2 Å to 60 Å (Angstrom) wasdisclosed for hemoperfusion by Clark (U.S. Pat. No. 4,048,064; 1977).This pore size range was primarily specified for detoxification andpreventing adsorption of anticoagulants, platelets and leukocytes fromthe blood but is inadequate for adsorbing midsize proteins such ascytochrome-c and beta-2-microglobulin. Similarly, coating inorganicadsorbents, such as silicate and diatomite, with a membrane film havingpore sizes greater than 20 Å was disclosed by Mazid (U.S. Pat. No.5,149,425; 1992) for preparing hemoperfusion adsorbents. More recently,Giebelhausen (U.S. Pat. No. 551,700; 2003) disclosed a sphericaladsorbent with pronounced microstructure with 0-40 Å pore diameters andan overall micropore volume of at least 0.6 cm³/g for adsorption ofchemical warfare agents, toxic gases and vapors, and refrigeratingagents. The above pore structures are too small for adsorption ofmidsize proteins from physiologic fluids.

An adsorbent with a broad distribution of pore sizes (40-9,000 Ådiameter) was disclosed for adsorbing proteins, enzymes, antigens, andantibodies by Miyake et al. (U.S. Pat. No. 4,246,351; 1981). Theadsorbent sorbs both the toxins as well as the beneficial proteins suchas albumin from the blood due to its broad pore size distribution.Immobilizing antibodies and IgG-binding proteins onto porous polymericadsorbents were described to enhance selectivity of adsorbents havingbroad pore size distributions for lowering low density lipoproteins, fortreating atherosclerosis, for adsorbing rheumatoid arthritis factor(Strahilevitz, U.S. Pat. No. 6,676,622; 2004), and for removinghepatitis C virus from blood (Ogino et al. U.S. Pat. No. 6,600,014;2003). The antibodies or proteins bound to adsorbents, however, couldgreatly increase the side effects for a hemoperfusion or a plasmaperfusion device and could greatly increase the difficulty formaintaining sterility of the devices.

Removal of beta-2-microglobulin by direct hemoperfusion was beneficialto renal patients (Kazama, “Nephrol. Dial. Transplant”, 2001, 16:31-35).An adsorbent with an enhanced portion of pores in a diameter rangebetween 10 and 100 Å was described by Braverman et al. (U.S. Pat. No.5,904,663; 1999) for removing beta-2-microglobulin from blood and byDavankov et al (U.S. Pat. No. 6,527,735; 2003) for removing toxins inthe molecular weight range of 300-30,000 daltons from a physiologicfluid. Strom, et al. (U.S. Pat. No. 6,338,801; 2002) described asynthesis method for polymer resins with pore sizes in the range from 20Å to 500 Å intended for adsorbing beta-2-microglobulin. The in-vitrostudy by the present inventors shows that the pore structures proposedby Davankov and Strom, however, are inadequate for a selectiveadsorption of midsize proteins such as beta-2-microglobulin andcytochrome-c in the presence of serum albumin.

In contrast to prior disclosures, the porous polymeric adsorbentsspecified in the present invention demonstrate a high selectivity foradsorbing small and midsize proteins to the exclusion of the largeproteins with molecular weights greater than 50,000 daltons. Moresignificantly, the present invention discloses adsorbents forhemoperfusion suitable for long term clinical treatment, since thehealthy components such as albumin, red blood cells, platelets and whiteblood cells are maintained at clinically acceptable levels.

SUMMARY OF INVENTION

In one embodiment, the present invention provides for a polymer systemcomprising at least one polymer with a plurality of pores, and thepolymer has at least one transport pore with a diameter from about 250Angstroms to about 2000 Angstroms, and the polymer has a transport porevolume greater than about 1.8% to about 78% of a capacity pore of volumeof the polymer.

For purposes of this invention, the term “transport pore” is defined asa pore that allows for a fast “transport” of the molecules to theeffective pores and the term “transport pore volume” means the volume ofthe “transport” pores per unit mass of the polymer.

In another embodiment, the pores have diameters from greater than 100Angstrom to about 2000 Angstrom. In yet another embodiment, the polymeris capable of sorbing protein molecules greater than 20,000 to less than50,000 Daltons from blood and excluding the sorption of blood proteinsgreater than 50,000 Daltons.

In still another embodiment, the polymer has a pore volume from about0.315 cc/g to about 1.516 cc/g. In still yet another embodiment, thepolymer has effective pore volume greater than from about 21.97% toabout 98.16% of the capacity pore volume. In a further embodiment, thepolymer comprises effective pores, said effective pores having adiameter from greater than about 100 Angstroms to about 250 Angstroms.

For purposes of this invention, the term “total pore volume” is definedas the volume of all the pores in a polymer per unit mass and the term“effective pore volume” means any pore which is selective adsorption ofmolecules. The term “capacity pore volume” is defined as the volume ofthe “capacity” of all the pores per unit mass of polymer and the term“effective pores” means the functional pores designed to adsorbparticular molecules. The term “capacity pore” is the total sum of theeffective pores and transport pores. For purposes of this invention, theterm “capacity pore volume is the volume of all the effective pores andtransport pores per unit of polymer.

In another further embodiment, the polymer is biocompatible. In yetanother embodiment, the polymer is hemocompatible. In still a furtherembodiment, the geometry of the polymer is a spherical bead.

In yet a further embodiment, the polymer is used in direct contact withwhole blood to sorb protein molecules selected from a group consistingessentially of cytokines and β₂-microglobulin and exclude the sorptionof large blood proteins, and the large blood proteins are selected froma group consisting essentially of hemoglobin, albumin, immunoglobulins,fibrinogen, serum proteins and other blood proteins larger than 50,000Daltons.

In still yet a further embodiment, the polymer has an internal surfaceselectivity for adsorbing proteins smaller than 50,000 Daltons, havinglittle to no selectivity for adsorbing vitamins, glucose, electrolytes,fats, and other hydrophilic small molecular nutrients carried by theblood.

In another embodiment, the polymer is made using suspensionpolymerization. In still another embodiment, the polymer is constructedfrom aromatic monomers of styrene and ethylvinylbenzene with acrosslinking agent selected from a group consisting essentially ofdivinylbenzene, trivinylcyclohexane, trivinylbenzene,divinylnaphthalene, divinylsulfone, trimethylolpropane triacrylate,trimethylolpropane trimethacrylate and mixtures thereof.

In another embodiment, the crosslinking agent is DVD in amount fromabout 20% to about 90% of the polymer.

In yet another embodiment, the stabilizing agent for the dropletsuspension polymerization is selected from a group consistingessentially of hemocompatibilizing polymers, said polymers beingpoly(N-vinylpyrrolidinone), poly(hydroxyethyl acrylate),poly(hydroxyethyl methacrylate), hydroxylethyl cellulose, hydroxypropylcellulose, salts of poly(acrylic acid), salts of poly(methacrylic acid),poly(dimethylaminoethyl acrylate), poly(dimethylaminoethylmethacrylate), poly(diethylaminoethyl acrylate), poly(diethylaminoethylmethacrylate), poly(vinyl alcohol) and mixtures thereof.

In still yet another embodiment, the polymer is made hemocompatible byexterior coatings selected from a group consisting essentially ofpoly(N-vinylpyrrolidinone), poly(hydroxyethyl acrylate),poly(hydroxyethyl methacrylate), hydroxyethyl cellulose, hydroxypropylcellulose, salts of poly(acrylic acid), salts of poly(methacrylic acid),poly(dimethylaminoethyl methacrylate), poly(dimethylaminoethylacrylate), poly(diethylaminoethyl acrylate), poly(diethylaminoethylmethacrylate), poly(vinyl alcohol) and mixtures thereof.

In a further embodiment, the polymer is made hemocompatible by surfacegrafting of the hemocompatible exterior coatings concomitantly withformation of the porous polymer beads.

In another further embodiment, the polymer is made hemocompatible bysurface grafting of the hemocompatible exterior coatings onto thepreformed porous polymeric beads.

In still another further embodiment, the polymer has an external surfacewith a negative ionic charge, and the negative ionic charge preventsalbumin from entering said pores.

In yet another further embodiment, the present invention relates to asize selective polymer comprising at least one polymer with a pluralityof pores, and the pores have diameters from greater than 100 Angstrom toabout 2000 Angstrom, and the polymer has a transport pore volume greaterthan about 1.8% to about 78% of a capacity pore of volume of thepolymer.

In still yet another further embodiment, the present invention providesfor a size selective polymer comprising a plurality of pores, and thepores have diameters from greater than 100 Angstrom to about 2000Angstrom, and the polymer has at least one transport pore with adiameter from about 250 Angstroms to about 2000 Angstroms, and thepolymer has an external surface with a negative ionic charge, and thenegative ionic charge prevents albumin from entering said pores at a pHfrom about 7.2 to about 7.6.

In one embodiment, the present invention relates to a porous polymer forsorbing small to midsize protein molecules and excluding sorption oflarge blood proteins, the polymer comprising a plurality of pores. Thepores sorb small to midsize protein molecules equal to or less than50,000 Daltons. In another embodiment, the polymer is biocompatibleand/or hemocompatible.

In yet another embodiment, the polymer comprises a plurality of poreswith diameters from about 75 Angstrom to about 300 Angstrom. In anotherembodiment, the polymer can have a plurality of pores within the aboverange. In another further embodiment, the polymer has its working poreswithin the above mentioned range and can also have non-working poresbelow the 75 Angstrom range. In another embodiment, the polymer has nomore than 2.0 volume % of its total pore volume in pores with diametersgreater than 300 Angstroms. For purposes of this invention, the term“large blood proteins” is defined as any blood protein greater than50,000 Daltons in size and the term “blood protein molecules” relates tosmall to midsize blood proteins equal to or less than 50,000 Daltons.

In still yet another embodiment, the geometry of the polymer is aspherical bead. In a further embodiment, the polymer has a pore volumegreater than 98.0% in pores smaller than 300 Angstroms diameter.

In another further embodiment, the polymer is used in direct contactwith whole blood to adsorb protein molecules such as β₂-microglobulinbut excluding the sorption of larger blood proteins, said large bloodproteins being selected from a group consisting essentially ofhemoglobin, albumin, immunoglobulins, fibrinogen, serum proteins largerthan 50,000 Daltons and mixtures thereof. In yet another furtherembodiment, the polymer has an internal surface selectivity foradsorbing proteins smaller than 50,000 Daltons, having little to noselectivity for adsorbing vitamins, glucose, electrolytes, fats, andother hydrophilic small molecular nutrients carried by the blood.

In still a further embodiment, the polymer is made porous usingmacroreticular synthesis or macronet synthesis. In still yet a furtherembodiment, the polymer is made using suspension polymerization.

In another embodiment, the polymer is constructed from aromatic monomersof styrene and ethylvinylbenzene with crosslinking provided bydivinylbenzene, trivinylcyclohexane, trivinylbenzene,divinylnaphthalene, divinylsulfone, trimethylolpropane triacrylate,trimethylolpropane trimethacrylate and mixtures thereof.

In yet another embodiment, the stabilizing agent for the dropletsuspension polymerization is selected from a group consistingessentially of hemocompatibilizing polymers, said polymers beingpoly(N-vinylpyrrolidinone), poly(hydroxyethyl acrylate),poly(hydroxyethyl methacrylate), hydroxylethyl cellulose, hydroxypropylcellulose, salts of poly(acrylic acid), salts of poly(methacrylic acid),poly(dimethylaminoethyl acrylate), poly(dimethylaminoethylmethacrylate), poly(diethylaminoethyl acrylate), poly(diethylaminoethylmethacrylate), poly(vinyl alcohol) and mixtures thereof.

In still another embodiment, the polymer is made hemocompatible byexterior coatings of poly(N-vinylpyrrolidinone), poly(hydroxyethylacrylate), poly(hydroxyethyl methacrylate), hydroxyethyl cellulose,hydroxypropyl cellulose, salts of poly(acrylic acid), salts ofpoly(methacrylic acid), poly(dimethylaminoethyl methacrylate),poly(dimethylaminoethyl acrylate), poly(diethylaminoethyl acrylate),poly(diethylaminoethyl methacrylate), poly(vinyl alcohol) and mixturesthereof.

In yet another embodiment, the polymer is made hemocompatible by surfacegrafting of the hemocompatible exterior coatings concomitantly withformation of the porous polymer beads. In still yet another embodiment,the polymer is made hemocompatible by surface grafting of thehemocompatible exterior coatings onto the preformed porous polymericbeads.

In a further embodiment, the present invention relates to a polymerabsorbent for excluding albumin from sorption. The polymer comprisespores with diameters from about 75 Angstrom to about 300 Angstrom.

In another further embodiment, the present invention provides ahemocompatible polymer comprising a working pore range. The working porerange has pore diameters from about 75 Angstrom to about 300 Angstromand the polymer is designed to adsorb blood protein molecules.

In another embodiment, the present invention relates to a size selectivepolymer for sorbing small to midsize blood borne proteins and excludingthe sorption of large blood borne proteins; the polymer comprises aplurality of pores, and the pores have diameters from about 75 Angstromto about 300 Angstrom. The polymer is used in direct contact with wholeblood to adsorb cytokines and β₂-microglobulin but excludes theadsorption of large blood borne proteins, and the large blood borneproteins are selected from a group consisting essentially of hemoglobin,albumin, immunoglobulins, fibrinogen, serum proteins larger than 50,000Daltons and mixtures thereof. For purposes of this invention, the term“blood borne proteins” includes enzymes, hormones and regulatoryproteins such as cytokines and chemokines.

The present invention discloses size-selective, biocompatible, andhemocompatible porous polymeric adsorbents whose pore structures aredesigned for efficacy in hemoperfusion. For efficacy in hemoperfusion,the adsorbents must sorb proteins selectively over the other smallmolecular species and the hydrophilic molecules present in blood. Theprotein sorption must also be restricted to molecular sizes smaller than50,000 daltons so that the important proteins required for healthhomeostasis—albumin, immunoglobulins, fibrinogen—remain in the bloodduring the hemoperfusion treatment.

The porous polymeric adsorbents of this invention have a hemocompatibleexterior surface coating and an internal pore system with an aromaticpore surface for protein selectivity. These porous polymeric adsorbentsexclude entrance into the pore system of protein molecules larger than50,000 Daltons but provide good mass transport into the pore system forthe protein molecules with sizes smaller than 35,000 Daltons.

The porous polymers of this invention are constructed from aromaticmonomers of styrene and ethylvinylbenzene with crosslinking provided byone of the following or mixtures of the following of divinylbenzene,trivinylcyclohexane, trimethylolpropane triacrylate andtrimethylolpropane trimethacrylate. Other crosslinking agents that maybe used to construct the porous polymeric adsorbents of this inventionare divinylnaphthalene, trivinylbenzene and divinylsulfone and mixturesthereof.

In another embodiment, the polymer adsorber is synthesized by an organicsolution in which 25 mole % to 90 mole % of the monomer is crosslinkingagents such as divinylbenzene and trivinylbenzene, and the resultingpolymer adsorber has a sufficient structural strength.

The porous polymers of this invention are made by suspensionpolymerization in a formulated aqueous phase with free radicalinitiation in the presence of aqueous phase dispersants that areselected to provide a biocompatible and a hemocompatible exteriorsurface to the formed polymer beads. The beads are made porous by themacroreticular synthesis with an appropriately selected porogen(precipitant) and an appropriate time-temperature profile for thepolymerization in order to develop the proper pore structure.

Porous beads are also made with small pore sizes by thehypercrosslinking methodology which is also known as macronetting or themacronet synthesis. In this methodology, a lightly crosslinked gelpolymer—crosslinking usually less than two (2) wt. %—is swelled in agood difunctional swelling agent for the polymeric matrix. In theswollen state, the polymeric matrix is crosslinked by a catalyzedreaction. The catalyzed reaction is most often a Friedel-Crafts reactioncatalyzed by a Lewis-acid catalyst. The resulting product is amacroporous polymer which is a crosslinked polymer having a permanentpore structure in a dry, non-swollen state.

For the purposes of this invention, the term “biocompatible” is definedas a condition of compatibility with physiologic fluids withoutproducing unacceptable clinical changes within the physiologic fluids.The term “hemocompatible” is defined as a condition whereby a materialwhen placed in contact with whole blood or blood plasma results inclinically acceptable physiologic changes.

The biocompatible and hemocompatible exterior surface coatings on thepolymer beads are covalently bound to the bead surface by free-radicalgrafting. The free-radical grafting occurs during the transformation ofthe monomer droplets into polymer beads. The dispersant coating andstabilizing the monomer droplets becomes covalently bound to the dropletsurface as the monomers within the droplets polymerize and are convertedinto polymer. Biocompatible and hemocompatible exterior surface coatingscan be covalently grafted onto the preformed polymer beads if thedispersant used in the suspension polymerization is not one that impartsbiocompatibility or hemocompatibility. Grafting of biocompatible andhemocompatible coatings onto preformed polymer beads is carried out byactivating free-radical initiators in the presence of either themonomers or low molecular weight oligomers of the polymers that impartbiocompatibility or hemocompatibility to the surface coating.

Biocompatible and hemocompatible exterior surface coatings on polymerbeads are provided by a group of polymers consisting ofpoly(N-vinylpyrrolidinone), poly(hydroxyethyl methacrylate),poly(hydroxyethyl acrylate), hydroxyethyl cellulose, hydroxypropylcellulose, salts of poly(acrylic acid), salts of poly(methacrylic acid),poly(dimethylaminoethyl methacrylate), poly(dimethylamnoethyl acrylate),poly(diethylaminoethyl acrylate), poly(diethylaminoethyl methacrylate),and poly(vinyl alcohol).

In one embodiment, the exterior surface coatings such aspoly(methacrylate) and poly(acrylate) polymers form anionic ions at pH7.2 to 7.6 and the said exterior surface expel albumin which carries anet negative ionic charge at normal blood pH (7.4) and inhibiting thealbumin from entering the pores at the exterior surface of the absorberby repulsion. In yet another embodiment, the thin layer external surfaceof the divinylbenzene copolymer is modified to become an anionicexchanger so that the external surface forms negative charges to expelthe albumin from entering the inner pores of the adsorber. Albumin hasan isoelectric point at pH 4.6 and has a net negative charge in normalpH of blood and other physiological fluid. With the negative charges onthe thin layer of the external surface of the adsorber, the pore sizelimitation can be expanded to a wider range while the said polymer stillexhibit a selectivity preference of adsorbing toxin to albumin.

The hemoperfusion and perfusion devices consist of a packed bead bed ofthe size-selective porous polymer beads in a flow-through containerfitted with a retainer screen at both the exit end and the entrance endto keep the bead bed within the container. The hemoperfusion andperfusion operations are performed by passing the whole blood, bloodplasma or physiologic fluid through the packed bead bed. During theperfusion through the bead bed, the protein molecules smaller than35,000 Daltons are extracted by adsorption while the remainder of thefluid components pass through essentially unchanged in concentration.

For the purposes of this invention, the term “perfusion” is defined aspassing a physiologic fluid by way of a suitable extracorporeal circuitthrough a device containing the porous polymeric adsorbent to removetoxins and proteins from the fluid. The term “hemoperfusion” is aspecial case of perfusion where the physiologic fluid is blood. The term“dispersant” or “dispersing agent” is defined as a substance thatimparts a stabilizing effect upon a finely divided array of immiscibleliquid droplets suspended in a fluidizing medium. The term“macroreticular synthesis” is defined as a polymerization of monomersinto polymer in the presence of an inert precipitant which forces thegrowing polymer molecules out of the monomer liquid at a certainmolecular size dictated by the phase equilibria to give solid nanosizedmicrogel particles of spherical or almost spherical symmetry packedtogether to give a bead with physical pores of an open cell structure[U.S. Pat. No. 4,297,220, Meitzner and Oline, Oct. 27, 1981; R. L.Albright, Reactive Polymers, 4, 155-174 (1986)]. For purposes of thisinvention, the term “sorb” is defined as “taking up and binding byabsorption and adsorption”.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention. These drawings are incorporatedin and constitute a part of this specification, illustrate one or moreembodiments of the present invention and together with the description,serve to explain the principles of the present invention.

FIG. 1 is a graph of Table 2 showing a plot of pore volume v porediameter (dV/dD vs. D) for Various Adsorbents Measured by NitrogenDesorption Isotherm.

Among those benefits and improvements that have been disclosed, otherobjects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings. The drawings constitute a part of this specification andinclude exemplary embodiments of the present invention and illustratevarious objects and features thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; it is to be understood that the disclosed embodiments are merelyexemplary of the invention that may be embodied in various forms.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limits, but merely as a basis for teachingone skilled in the art to employ the present invention. The specificexamples below will enable the invention to be better understood.However, they are given merely by way of guidance and do not imply anylimitation.

Five porous polymeric adsorbents are characterized for their porestructures and are assessed for their competitive adsorption ofcytochrome-c (11,685 Daltons in size) over serum albumin (66,462 Daltonsin size). The adsorbent syntheses are described in Example 1; the porestructure characterization is given in Example 2; the competitivedynamic adsorption procedure and results are provided in Example 3; andthe competitive efficacy for pick up the smaller cytochrome-c proteinover the larger albumin molecule is discussed under Example 4.

Example 1 Adsorbent Syntheses

The synthesis process consists of (1) preparing the aqueous phase, (2)preparing the organic phase, (3) carrying out the suspensionpolymerization, and (4) purifying the resulting porous polymericadsorbent product. The aqueous phase compositions are the same for allthe polymerizations. Table 1A lists the percentage composition of theaqueous phase and Table 1B gives the material charges typical for a five(5) liter-reactor polymerization run.

TABLE 1A Aqueous Phase Composition Wt. % Ultrapure Water 97.787Dispersing Agent: Polyvinylalcohol 0.290 Monosodium Phosphate 0.300Disodium Phosphate 1.000 Trisodium Phosphate 0.620 Sodium Nitrite 0.003

TABLE 1B Material Charges for a Typical Five (5) Liter-ReactorPolymerization Run Volume of Aqueous Phase 1750.00 ml Density of AqueousPhase 1.035 g/ml Weight of Aqueous Phase 1811.25 g Volumetric Ratio,Aqueous Phase/Organic Phase 1.05 Volume of Organic Phase 1665.0 mlDensity of Organic Phase 0.84093 g/ml Weight of Organic Phase, ExcludingInitiator Charge 1400.15 g Total Reaction Volume 3415.0 ml TotalReaction Weight 3211.40 g Initiator, Pure Benzoyl Peroxide (BPO) 8.07606g Initiator, 97% BPO 8.3258 g (Note: Initiator charge is calculated ononly the quantity of polymerizable monomers introduced into thereactor.) Commercial 63% Divinylbenzene (DVB) 794.814 g [98.65Polymerizable Monomers of DVB and EVB (Ethylvinylbenzene); 1.35% inertcompounds; 63.17% DVB; 35.48% EVB] Toluene 269.300 g Isooctane 336.036 gBenzoyl Peroxide, 97% 8.3258 g Total, Organic Charge 1408.4758 g

Upon preparation of the aqueous phase and the organic phase, the aqueousphase is poured into the five-liter reactor and heated to 65° C. withagitation. The pre-mixed organic phase including the initiator is pouredinto the reactor onto the aqueous phase with the stirring speed set atthe rpm for formation of the appropriate droplet size. The dispersion oforganic droplets is heated to the temperature selected for thepolymerization and is held at this temperature for the desired length oftime to complete the conversion of the monomers into the crosslinkedpolymer and, thereby, set the pore structure. Unreacted initiator isdestroyed by heating the bead slurry for two (2) hours at a temperaturewhere the initiator half-life is one hour or less. For the initiator,benzoyl peroxide, the unreacted initiator is destroyed by heating theslurry at 95° C. for two (2) hours.

The slurry is cooled, the mother liquor is siphoned from the beads andthe beads are washed five (5) times with ultrapure water. The beads arefreed of porogen and other organic compounds by a thermal cleaningtechnique. This process results in a clean, dry porous adsorbent in theform of spherical, porous polymer beads.

TABLE 1C Components of Adsorbent Syntheses Porous Polymer IdentityAdsorbent 1 Adsorbent 3 Adsorbent 4 Adsorbent 5 Wt. %^(a) Adsorbent 2Wt. %^(a) Wt. %^(a) Wt. %^(a) Divinylbenzene, 35.859 Adsorbent 2 is a26.163 22.4127 22.4127 (DVB), Pure comercial resin, Ethylvinylbenzene20.141 Amberlite 14.695 12.5883 12.5883 (EVB), Pure XAD-16 ®, madeInerts 0.766 by Rohm and 0.559 0.4790 0.4790 Haas Company Toluene 19.23427.263 64.521 54.841 Isooctane 24.00 31.319 0.00 9.680 Polymerizable56.00 40.8584 35.00 35.00 Monomers Porogen 44.00 59.1416 65.00 65.00Benzoyl Peroxide 1.03 0.7447 2.00 4.00 (BPO), Pure; Wt. % Based UponPolymerizable Monomer Content Polymerization, 75°/10 hrs 80°/16 hrs70°/24 hrs 65°/24 hrs ° C./time, hrs. 95°/2 hrs  95°/2 hrs  ^(a)Wt. %value is based upon the total weight of the organic phase excluding theinitiator.

Example 2 Pore Structure Characterization

The pore structures of the adsorbent polymer beds identified in TABLE 1Cwere analyzed with a Micromeritics ASAP 2010 instrument. The results areprovided in GRAPH 1 where the pore volume is plotted as a function ofthe pore diameter. This graph displays the pore volume distributionacross the range of pore sizes.

The pore volume is divided up into categories within pore size rangesfor each of the five adsorbent polymers and these values are provided inTABLE 2. The Capacity Pore Volume is that pore volume that is accessibleto protein sorption and consists of the pore volume in pores larger than100 Å diameter. The Effective Pore Volume is that pore volume that isselectively accessible to proteins smaller than 35,000 Daltons andconsists of pore diameters within the range of 100 to 250 Å diameter.The Oversized Pore Volume is the pore volume accessible to proteinslarger than 35,000 Daltons and consists of the pore volume in poreslarger than 250 Å diameter. The Undersize Pore Volume is the pore volumein pores smaller than 100 Å diameter and is not accessible to proteinslarger than about 10,000 Daltons.

TABLE 2 Pore Structures of Adsorbents Polymer Adsorber ID AdsorbentAdsorbent Adsorbent Adsorbent Adsorbent 1 2 3 4 5 Capacity Pore Volume,0.5850 1.2450 1.5156 0.3148 0.6854 cc/g; Dp, 100 Å→2000 Å Effective PoreVolume, 0.5678 0.9860 0.3330 0.3060 0.6728 cc/g; Dp, 100 Å→250 ÅTransport Pore Volume of 0.0172 0.2590 1.1826 0.0088 0.0126 Dp =250~2000 Å, cc/g Effective Pore (100~250 Å)Volume, 97.06% 79.20% 21.97%97.20% 98.16% as % of capacity pore Transport Pore (250~2000 Å) Volume,2.9% 20.8% 78.0% 2.8% 1.8% as % of capacity pore Undersized Pore Volume,0.3941 0.5340 0.4068 0.6311 0.4716 cc/g; Dp < 100 Å Total Pore Volume,cc/g; 0.9792 1.7790 1.9225 0.9459 1.1569 Dp, 17 Å→2000 Å Pore Vol (cc/g)of Dp = 500 Å to 2,000 Å 0.0066 0.016 0.668 0.0036 0.0053 Volune ofPores in 100~750 Å, cc/g 0.5816 1.2357 1.4915 0.3133 0.6825 Volume ofPores in 100~750 Å, as % of 99.4% 99.3% 98.4% 99.5% 99.6% capacity poreDp = Pore Diameter in Å (Angstrom)

FIG. 1 depicts a Graph of Table 2 showing a plot of pore volume v porediameter (dV/dD vs. D) for Various Adsorbents Measured by NitrogenDesorption Isotherm.

Example 3 Protein Adsorption Selectivity

The polymeric adsorbent beads produced in Example 1 are wetted out withan aqueous solution of 20 wt. % isopropyl alcohol and thoroughly washedwith ultrapure water. The beads with diameters within 300 to 850 micronsare packed into a 200 ml hemoperfusion device which is a cylindricalcartridge 5.4 cm in inside diameter and 8.7 cm in length. The beads areretained within the cartridge by screens at each end with an orificesize of 200 microns. End caps with a center luer port are threaded ontoeach end to secure the screens and to provide for fluid distribution andattachment for tubing.

Four liters of an aqueous 0.9% saline solution buffered to a pH of 7.4are prepared with 50 mg/liter of horse heart cytochrome-c and 30 g/literof serum albumin. These concentrations are chosen to simulate a clinicaltreatment of a typical renal patient where albumin is abundant andβ₂-microglobulin is at much lower levels in their blood. Horse heartcytochrome-c with a molecular weight 11,685 daltons has a molecular sizevery close to β₂-microglobulin at 11,845 daltons and, therefore, ischosen as the surrogate for β₂-microglobulin. Serum albumin is a muchlarger molecule than cytochrome-c with a molecular weight of 66,462daltons and, therefore, allows for the appropriate competitiveadsorption studies needed for selecting the porous polymer with theoptimum pore structure for size-selective exclusion of albumin.

The protein solution is circulated by a dialysis pump from a reservoirthrough a flow-through UV spectrophotometer cell, the bead bed, andreturned to the reservoir. The pumping rate is 400 ml/minute for aduration of four (4) hours. The concentration of both proteins in thereservoir is measured periodically by their UV absorbance at 408 nm forcytochrome-c and at 279 nm for albumin.

All five adsorbents identified in TABLE 1C were examined by thiscompetitive protein sorption assessment and the measured results aregiven in TABLE 3.

TABLE 3 Size-Selective Efficacy of Porous Polymeric Adsorbents PolymerAdsorber ID Adsorbent Adsorbent Adsorbent Adsorbent Adsorbent 1 2 3 4 5Capacity Pore Volume, 0.5850 1.2450 1.5156 0.3148 0.6854 cc/g; Dp, 100Å→2000 Å Effective Pore Volume, 0.5678 0.9860 0.3330 0.3060 0.6728 cc/g;Dp, 100 Å→250 Å Transport Pore Volume of 0.0172 0.2590 1.1826 0.00880.0126 Dp = 250~2000 Å, cc/g Effective Pore (100~250 Å)Volume, 97.06%79.20% 21.97%   97.20% 98.16% as % of capacity pore Transport Pore(250~2000 Å) Volume, 2.9% 20.8% 78.0%   2.8% 1.8% as % of capacity poreUndersized Pore Volume, 0.3941 0.5340 0.4068 0.6311 0.4716 cc/g; Dp <100 Å Total Pore Volume, cc/g; 0.9792 1.7790 1.9225 0.9459 1.1569 Dp, 17Å→2000 Å Pore Vol (cc/g) of Dp = 500 Å to 2,000 Å 0.0066 0.016 0.668 0.0036 0.0053 Volune of Pores in 100~750 Å, cc/g 0.5816 1.2357 1.49150.3133 0.6825 Volume of Pores in 100~750 Å, as % of 99.4% 99.3% 98.4%  99.5% 99.6% capacity pore % Cytochrome-C, Adsorbed 89.0% 96.7% 95.3%  57.4% 90.1% % Albumin Adsorbed 3.7% 8.1% 13%     1.0% 1.8% Selectivity24.05 11.94 7.27  57.1 50.06 Dp = Pore Diameter in Å (Angstrom)

Example 4 Pore Volume and Pore Size Range for Suitable Kinetics andSize-Selectivity for Cytochrome-C Over Albumin

TABLE 3 and GRAPH 1 summarize the pertinent pore structure data and theprotein perfusion results carried out on all five (5) adsorbents. Theselectivity for adsorbing cytochrome-c over albumin decreased in thefollowing order: Adsorbent 4>Adsorbent 5>Adsorbent 1>Adsorbent2>Adsorbent 3.

The quantity of cytochrome-c adsorbed during the four hour perfusiondecreased in the following order: Adsorbent 2>Adsorbent 3>Adsorbent5>Adsorbent 1>Adsorbent 4.

Adsorbent 4 with the highest selectivity at 57.1 had the poorestkinetics picking up only 57.4% of the available cytochrome-c over thefour hour perfusion. This kinetic result occurs from the Effective PoreVolume being located at the small end of the pore size range, having allits Effective Pore Volume within the pore size range of 130 to 100 Å.There is insignificant pore volume in pores larger than 130 Å and thissmall pore size retards the ingress of cytochrome-c.

Adsorbent 5 with its major pore volume between 100 to 200 Å had thesecond highest selectivity for cytochrome-c over albumin at 50.6 and ithad good mass transport into the Effective Pore Volume pores picking up90.1% of the cytochrome-c during the four hour perfusion. This porouspolymer has the best balance of properties with excellentsize-selectivity for cytochrome-c over albumin and very good capacityfor cytochrome-c during a four hour perfusion.

Adsorbent 1 showed reasonably good selectivity at 24.05 for sorbingcytochrome-c over albumin. It also exhibited good capacity for sorbingcytochrome-c during the four hour perfusion, picking up 89.0% of thequantity available.

Adsorbent 2 with the highest capacity for sorbing cytochrome-c duringthe four hour perfusion picked up 96.7% of the available cytochrome-c.This high capacity arises from having a large pore volume, 0.986 cc/g,and within the Effective Pore Volume range of 100 Å to 250 Å. However,this porous polymer allowed more albumin to be adsorbed than Adsorbents1, 4, and 5, since it has significant pore volume, 0.250 cc/g, in thepore size group from 250 Å to 300 Å.

Adsorbent 3 with a very broad pore size distribution (see GRAPH 1) hadthe poorest selectivity among the group at 7.27. It has a very largepore volume in the pore size range larger than 250 Å. This porouspolymer has a pore volume of 1.15 cc/g within the pore size range of 250Å to 740 Å. In contrast with the other four adsorbents, this porouspolymer is not size-selective for proteins smaller than about 150,000Daltons, although it did sorb 95.3% of the available cytochrome-c duringthe perfusion.

On balance of properties of selectively for sorbing cytochrome-c overalbumin and its capacity for picking up cytochrome-c during a four hourperfusion, porous polymeric Adsorbent 5, gave the best performance. Thisporous polymer has the proper pore structure to perform well inhemoperfusion in concert with hemodialysis for people with End StageRenal Disease.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the attendant claims attachedhereto, this invention may be practiced other than as specificallydisclosed herein.

1. A polymer system consisting of polymers defining a porous structure wherein the porous structure consists of pores with diameters in the range of 17 Angstroms to about 2000 Angstroms, said porous structure comprising transport pores with diameters from about 250 Angstroms to about 2000 Angstroms and effective pores with diameters greater than 100 Angstroms to about 250 Angstroms, said polymer system having a transport pore volume greater than about 1.8 to about 78% of a capacity pore volume of said system and an effective pore volume greater than about 22 to less than about 98.2% of the capacity pore volume.
 2. The system of claim 1 wherein said pores are measured using a micromeretics ASAP 2010 porisimeter.
 3. The system of claim 1 wherein said polymer system is capable of sorbing protein molecules greater than 20,000 to less than 50,000 Daltons from blood and excluding the sorption of blood proteins greater than 50,000 Daltons.
 4. The system of claim 1 wherein said polymer system has a total pore volume from about 0.315 cc/g to about 1.516 cc/g.
 5. The polymer system of claim 1 wherein said polymers are biocompatible.
 6. The polymer system of claim 1 wherein said polymers are hemocompatible.
 7. The polymer system of claim 1 wherein the geometry of said polymer system is a spherical bead.
 8. The polymer system of claim 1 wherein said polymer system is used in direct contact with whole blood to sorb protein molecules selected from a group consisting essentially of cytokines and β₂-microglobulin and exclude the sorption of large blood proteins, said large blood proteins being selected from a group consisting essentially of hemoglobin, albumin, immunoglobulins, fibrinogen, serum proteins and other blood proteins larger than 50,000 Daltons.
 9. The polymer system of claim 1 wherein said polymer system has an internal surface selectivity for adsorbing proteins smaller than 50,000 Daltons, having little to no selectivity for adsorbing vitamins, glucose, electrolytes, fats, and other hydrophilic small molecular nutrients carried by the blood.
 10. The polymer system of claim 1 wherein said polymer system is made using suspension polymerization.
 11. The polymer system of claim 1 wherein said polymers are constructed from aromatic monomers of styrene and ethylvinylbenzene with a crosslinking agent selected from a group consisting essentially of divinylbenzene, trivinylcyclohexane, trivinylbenzene, divinylnaphthalene, divinylsulfone, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and mixtures thereof.
 12. The polymer system of claim 1 wherein the polymer system is made using droplet suspension polymerization using a stabilizing agent selected from a group consisting essentially of hemocompatibilizing polymers, said polymers being poly(N-vinylpyrrolidinone), poly(hydroxyethyl acrylate), poly(hydroxyethyl methacrylate), hydroxylethyl cellulose, hydroxypropyl cellulose, salts of poly(acrylic acid), salts of poly(methacrylic acid), poly(dimethylaminoethyl acrylate), poly(dimethylaminoethyl methacrylate), poly(diethylaminoethyl acrylate), poly(diethylaminoethyl methacrylate), poly(vinyl alcohol) and mixtures thereof.
 13. The polymer system of claim 1 wherein said polymers are made hemocompatible by exterior coatings selected from a group consisting essentially of poly(N-vinylpyrrolidinone), poly(hydroxyethyl acrylate), poly(hydroxyethyl methacrylate), hydroxyethyl cellulose, hydroxypropyl cellulose, salts of poly(acrylic acid), salts of poly(methacrylic acid), poly(dimethylaminoethyl methacrylate), poly(dimethylaminoethyl acrylate), poly(diethylaminoethyl acrylate), poly(diethylaminoethyl methacrylate), poly(vinyl alcohol) and mixtures thereof.
 14. The polymer system of claim 13 wherein said polymers are made hemocompatible by surface grafting of the hemocompatible exterior coatings concomitantly with formation of the polymer system.
 15. The polymer system of claim 13 wherein said polymers are made hemocompatible by surface grafting of the hemocompatible exterior coatings onto the preformed polymer system.
 16. The polymer system of claim 1 wherein said polymers have an external surface with a negative ionic charge, said negative ionic charge prevents albumin from entering said pores.
 17. A size selective polymer defining a porous structure wherein the porous structure consists of pores with diameters in the range of 17 Angstroms to about 2000 Angstroms, said porous structure comprising transport pores with diameters from about 250 Angstroms to about 2000 Angstroms and effective pores with diameters greater than 100 Angstroms to about 250 Angstroms, said porous structure having a transport pore volume greater than about 1.8 to about 78% of a capacity pore volume of said porous structure and an effective pore volume greater than about 22 to less than about 98.2% of the capacity pore volume.
 18. A size selective polymer system consisting of polymers defining a porous structure wherein the porous structure consists of pores with diameters in the range of 17 Angstroms to about 2000 Angstroms, said porous structure comprising transport pores with diameters from about 250 Angstroms to about 2000 Angstroms and effective pores with diameters greater than 100 Angstroms to about 250 Angstroms, said polymer system having a transport pore volume greater than about 1.8 to about 78% of a capacity pore volume of said system and an effective pore volume greater than about 22 to less than about 98.2% of the capacity pore volume, said polymer has an external surface with a negative ionic charge, said negative ionic charge prevents albumin from entering said pores.
 19. The polymer of claim 17 wherein said pores are measured using a micromeretics ASAP 2010 porisimeter.
 20. The polymer of claim 18 wherein said pores are measured using a micromeretics ASAP 2010 porisimeter. 